The low point served as a wake-up call for Sabatier, who took an image of his balance and set a goal of saving so much money that he could retire early if he wanted to.

"I remember having this intense feeling of honestly just . . . lack of control," says Sabatier, who is now 32 and writes about his financial habits and mistakes on his blog, Millennial Money. "I never wanted to feel that way again."

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Now Sabatier runs multiple businesses. But his savings give him the leeway to be selective about the projects he takes on.

Sabatier found a job at a marketing agency, took on side gigs to make extra cash and managed to stash away as much as half of his pay cheque. He perused more than 300 personal finance books. And he reached his goal of saving $US1 million ($1.3 million) by age 30.

Now Sabatier, who lives with his wife in Chicago, runs multiple businesses. But his savings give him the leeway to be selective about the projects he takes on - and he can afford a lot more than that burrito he was craving all those years ago.

Here are some of his tips for boosting your savings, based on what worked for him - and the mistakes he's made along the way.

Find a side hustle

Sabatier "quickly realised" the $US50,000 he was earning at the marketing agency wasn't going to be enough for him to meet his saving goal. He started multiple side gigs to bring in extra money, such as launching a consulting company, selling concert tickets and building websites for businesses.

Sabatier later quit his 9-to-5 job at the agency so that he could dedicate more time to growing his website business, which was then earning him more money than his traditional day job.

Still, he kept up some of his other side hustles so that he could continue to save as much as possible. "If you just view your full-time job as the way you're going to get ahead, it's just going to take a lot longer," he says.

In his mission to make as much money as possible, Sabatier sacrificed a lot of time away from friends and family since he was spending the majority of his nights and weekends at work.

Make saving a daily habit

One of the most important habits Sabatier developed was to make his goal feel attainable.

Just because you can do something, doesn't mean that you should.

When Sabatier first decided to save more than $US1 million for retirement, the number was so large it felt beyond reach.

So he focused on the near-term and calculated that he could meet that goal in about 30 years if he saved at least $US50 a day and earned roughly 5 per cent a year.

"It's difficult for us to think about the future," he says. "So how do we bring the future into the present and use that to your advantage?"

He started off investing just $US5 a day through a brokerage app and increasing his contributions over time. But because he wanted to reach his savings goal as soon as possible, he didn't stop when he topped $US50 a day.

He stashed away any extra money that came in, such as a bonus or income from freelance work. And he reached the point where he was saving hundreds or thousands of dollars on some days.

Invest your extra cash

Sabatier says that he was only able to meet his goal because he invested the majority of his long-term savings in stocks and bonds, giving him a much higher return than he would have earned through a savings account.

This may seem obvious, but Sabatier's story is a reminder of how much money can be left on the table when people are too afraid to invest.

Part of his success comes from good timing: stocks have risen sharply since he doubled down on his savings goals during the financial crisis.

For example, savings invested in the Standard & Poor's 500-stock index when the market bottomed out in March 2009 would have tripled over the next eight years as the stock market recovered.

Meanwhile, cash put into a savings account over that same period would be virtually unchanged. (That said, financial advisers typically recommend that any money you'll need in the next couple of years should be kept in cash.)

Keep boosting your savings rate

As he earned more money from side gigs and reduced his living expenses, Sabatier moved from saving 15 per cent of his pay, to stashing 25 per cent and eventually saving more than 40 per cent of his pay cheque.

The idea of saving so aggressively may feel intimidating to some people, but even boosting your savings rate by a small amount can make a big difference over time, he says.

"Save $US20 more this week than you did last week," he says. "Or save 1 per cent more in your 401(k) [superannuation] every six months."

Sabatier at times reached the point where he felt like he was "saving too much", he wrote in his blog.

For a while, he stopped travelling, going out or even buying books. The sacrifices helped him build his nest egg. But the experience was a reminder that people should balance the expenses that are important to them, such as travelling to see family, with their saving goals.

Reduce your monthly expenses

As he became more serious about meeting his goals, Sabatier scaled back his monthly housing costs so that he could save even more.

He moved from a "really swanky apartment" in Chicago that cost about $US1500 a month to an apartment half the size that cost $US800 a month.

"That's $US700 more that went straight into my investment account," he says, adding that people should target the bills taking up the biggest share of their pay cheques.

Some people may find big savings from selling their car and eliminating monthly car payments, insurance bills and petrol costs, he says. Others may benefit from finding a roommate or renting out their apartments through websites such as Airbnb when they aren't home, Sabatier says.

Remember your goals

Years of living frugally and finding ways to make extra cash helped Sabatier meet his savings goal. But then last year he made a costly mistake: he got comfortable.

On the verge of splurging on a $US350 laptop bag, Sabatier realised that his spending was getting out of hand. He took a look at his transactions and calculated that he spent $US200,000 last year, more than twice as much as he had the year before. It became easy to spot some of the culprits: $US12,000 on a weekend in Napa Valley. Seventy-five dollars for takeout on a Wednesday night. Fifty dollars for a bottle of wine.

Sabatier knew that he could technically afford these things, but the "lifestyle inflation" he was experiencing could threaten the financial independence he had been working for.

"Just because you can do something, doesn't mean that you should," he says.

So far this year, he has tightened the reins on his spending. He is cooking more, buying $US12 bottles of wine and looking for cheaper accommodations when he travels.